Upper respiratory tract diseases (UPTD) are common in felines, especially domestic cats. These diseases exhibit influenza-like symptoms, including fever, nasal discharge, sneezing, coughing, sinusitis and bronchitis, and can potentially be fatal. The most common agents for UPTD include chlamydia, feline herpesvirus-1, feline calicivirus, and Bordetella bronchiseptica. More recently, felines have displayed susceptibility of infection to influenza viruses, especially the avian influenza virus (AIV).
AIV is an RNA virus belonging to the family of Orthomyxoviridae, and is classified as a type A influenza virus, which relates its nucleoprotein and membrane proteins. AIV has a lipid envelope that features two distinct glycoproteins: hemagglutinin (HA), which facilitates entry of the virus into the host cells, and neuraminidase (NA), which assists in the release of progeny virus from infected cells (de Jong et al., 2006). Thus far, 16 HA and 9 NA have been detected and can exist in varying combinations (Olsen et al., 2006), thereby forming subtypes of AIV that are based upon these antigenic differences. The H5N1 subtype (virus featuring HA 5 and NA 1) has specifically been associated with recent outbreaks in Asia, Russia, the Middle East, Europe and Africa, and is responsible for the growing concern of avian influenza infection of felids.
Reports regarding avian influenza infection of domestic cats and zoo felids emerged during the 2003 to 2004 avian influenza outbreak in Asia (Keawcharoen et al 2004). These reports described over 150 deaths of tigers and leopards as a result of feeding on raw chicken carcasses that were infected with the avian influenza. These felids developed lesions in the lungs, resulting in congestion and hemorrhaging, moderate meningoencephalitis, and mutifocal necrotizing hepatitis. Since then, scientists have confirmed that felines are susceptible to avian influenza infection via intratracheal injection, consumption of virus-infected chickens, and horizontal transmission through regular contact (Kuiken et al., 2004). The infected cats initially developed such symptoms as raised body temperature, conjunctivitis, and labored breathing, which eventually progressed to severe diffuse alveolar damage and death, although the virus can replicate in the respiratory tract without inducing any signs of the disease (Hinshaw et al. 1981). Further studies revealed that experimentally-infected cats displayed a presence of the virus in both respiratory and extra-respiratory organs, and excreted the virus through both the respiratory and digestive tracts (Rimmelzwaan et al., 2006). In addition, numerous new reports have described infection of domestic cats in Europe and Asia (Butler, 2006).
Considering the susceptibility of felines to AIV and their ability to excrete the virus into their surroundings, a method of preventing AIV infection and protecting felines is essential. The urgency is compounded given the possibility that feline infection may play a role in the epidemiology of AIV in poultry, humans, and other species (Influenza team, 2006; Kuiken et al., 2006). Accordingly, there is a need for an effective vaccine against influenza in felines.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.